Power supply control integrated circuits, especially those using current sense comparators, and even more so the ones for controlling power supplies in continuous conduction mode (CCM), are prone to false-triggering due to noise from adjacent switching circuits. Including two or more such controllers within one integrated circuit (IC) is problematic due to noise coupling and ground disturbances caused by an adjacent channel. A sub-optimal PCB layout can cause significant crosstalk in such multi-channel IC.
FIG. 1 depicts a prior art multi-channel peak current-mode control (CMC) IC 299 for driving a plurality of switching power converters 100. Each power converter 100 comprises a power inductor 101 operating in continuous conduction mode (CCM) or discontinuous conduction mode (DCM), a control switch 102 having a control gate input, a current sense resistor 104 for sensing current in the control switch 102, a freewheel diode 103 providing a path for the inductor 101 current when the switch 102 is off. The IC 299 comprises multiple peak CMC controllers 200, having an input for receiving current sense signal from the resistor 104, a driver output for controlling the gate input of the switch 102. Each controller 200 includes a comparator 201 having: an input for receiving current sense signal from the resistor 104; a reference input for receiving a reference voltage REF; and an output changing its level when the current sense signal 104 exceeds the reference REF. Each controller 200 also includes: a flip-flop circuit having an output Q for controlling the gate of the switch 102, a set input S for receiving a clock signal CLK, and a reset input R for receiving the output of the comparator 201.
FIG. 2 shows typical CCM waveforms 501 and 502 received at current sense inputs of the prior art IC 299 depicted in FIG. 1 from two resistors 104. With reference to waveform 501, in normal operation, the driver output turns the switch 102 off when the voltage at the corresponding resistor 104 exceeds REF. The switch 102 is turned on again when the clock signal CLK is received. However, with reference to waveform 502, switching transitions of the switch 102 generate disturbance 599 of current sense voltage 104 received by the adjacent controllers 200. This disturbance can cause false detection of the level REF, and the conduction cycle of the switch 104 can be terminated prematurely.
A method and a circuit are needed to eliminate these cross-coupling effects in a multi-channel power supply peak current-mode control IC, or any other type of power supply control ICs employing a current sense comparator 201.